As the number of hosts attached to a network increases beyond what can be
connected by a single local area network (LAN), forwarding packets between hosts
on different LANs becomes an issue. Two common solutions to the forwarding
problem are IP routing and spanning tree bridging. IP routing scales well, but
imposes the administrative burden of managing subnets and assigning addresses.
Spanning tree bridging, in contrast, requires no administration, but often does
not perform well in a large network, because too much traffic must detour toward
the root of the spanning tree, wasting link bandwidth.